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Teleportation of a qubit

  1. Jun 1, 2014 #1
    I have seen numerous articles referencing the teleportation of information over a distance of 3 meters using quantum entanglement.

    I don't believe it. That would contradict special relativity, would it not? You could, for example, decide which of two observers moving relatively to one another has the faster clock and which has the slower clock. One observer could encode the clock time into qubits and transmit them to the other. There would be no disagreement because quantum entanglement implies instantaneous correlation of states.

    I think they are only querying the state of a particle. Of course, they then know that same state will be realized instantaneously at the other end, but that does not permit the transmission of information, yet the "leader" of the project, Professor Hanson of Delft University, is quoted as saying that "in principle it should be possible to teleport ourselves from one place to another". That would necessarily involve the transformation of the information within a person's brain.
     
    Last edited: Jun 1, 2014
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  3. Jun 1, 2014 #2

    mfb

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    No. To transmit information, those teleportation mechanisms always have to send classical information as well - and that is not faster than the speed of light.
    In some (not all) interpretations of quantum mechanics, a part of the teleportation happens without delay (but even then you cannot tell in which frame it would happen without delay - every frame can share this view), but you cannot use this part alone for data transfer, for example.
    Right, and it would need a massive classical data transfer.
     
  4. Jun 2, 2014 #3
    I have two problems with your answer. First, directly from hansonlab.tudelft.nl/teleportation


    Second, there is a direct quote here from Hanson claiming secure communication.

    If the information is really being teleported and there's no way to intercept it, then a transmission through the EM field is not taking place. If it is also being transmitted through the EM field, then there is no 100% security.

    Here is how they claim to do it.

    I find this almost impossible to believe, especially because there is no claim of this being an exception to the principle of relativity, here or in any of the articles I have read.
     
  5. Jun 2, 2014 #4

    Nugatory

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    You might want to read the wikipedia article on quantum teleportation: http://en.wikipedia.org/wiki/Quantum_teleportation

    Mfb's answer is correct, and you are reading more into your material than is there.
     
  6. Jun 2, 2014 #5
    The popular articles are wrong. Information is not being teleported. The same random bit is being created simultaneously in two places. That is a useful thing to be able to do, but it ("quantum information") is not "information". It is just more sloppy physics terminology.
     
    Last edited: Jun 2, 2014
  7. Jun 3, 2014 #6

    mfb

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    Some of them are wrong, but the wikipedia page gives a good overview and has references to actual scientific articles.


    I guess you are talking about entanglement here, which you have to do prepare between some states before you can teleport things. But "the same random bit" is misleading, as this looks like a purely classical description. The bits are more than "just the same".

    Note that you cannot use "The same random bit is being created simultaneously in two places." to transmit any message. You know "hey, the other one sees the same bit", but you cannot fix this to a specific value. You can use it as secure one-time pad together with a classical channel.

    Let's send a message in that way:
    Yes, by performing quantum operations with the object to teleport and one entangled particle (in some interpretations of QM those involve instantaneous changes of the entangled partner).
    You cannot use this to send a message. Just with this, for every bit sent, the receiver gets 1 with 50% probability and 0 with 50% probability - it looks like purely random noise.

    To recover the message, the receiver has to know the result of measurements done at the sender - those results can be transferred in classical ways (electromagnetic waves, mail, avian carriers... does not matter). They alone also look like purely random noise. This is the 100% security part - it does not help you to intercept the classical data transfer.

    Only the combination of both - the teleported state and the classical data stream - allows a reconstruction of the message.

    If you want to transmit quantum states, the idea stays the same. You are not allowed to measure the transmitted particle (in the relevant parameter) as this will destroy the quantum state, but you still need the classical information path to prepare this state correctly.
     
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